Phonograph



E. O. THOMPSON raouommra Filed Sept. 18, 1940 4 Sheets-Sheet 1 Oct. 10,1944. E. o. THOMPSON PHONOGRAPH I Filed Sept. 18', 1940' 4 Sheets-Sheet2 Oct. 10, 1944. E. o. THOMPSON 2,359,808

PHONQGRAPH Filed Sept. 18. 1940 4 Sheets-Sheet 5 Patented Oct. 10, 1944PHONOGRAPH Elmer 0. Thompson,- Grasmere, N. Y., assignor to Philco Radioand Television Corporation, Philadelphia, Pa., a corporation of DelawareApplication September 18, 1944), Serial No. 357,322

15 Claims.

This invention relates to sound pick-up devices for phonographs, andmore particularly to devices of this class which are adapted for usewith an electronic amplifier in an audio frequency sound reproducingsystem. The invention is particularly directed to sound pick-up devicesemployed for example in radio-phonograph combinations, wherein the audiofrequency amplifier of the radio receiver is employed to amplifycurrents supplied thereto from the pick-up device.

The principal object of the invention is to provide an improved soundpick-13p device of the above mentioned character.

A more specific object of the invention is to provide a novel andimproved pick-up device of the above type employing a vibratory mirror,a light beam, and a photoelectric cell for translating the motion of thepick-up stylus into signal currents.

Another object of the invention is to provide an improved pick-up deviceof the above type adapted to greatly decrease record wear.

Another object of the invention is to provide a phonograph pick-upemploying a permanent stylus.

Another object of the invention is to provide a phonograph pick-uphaving a retractable stylus.

Still another object is to provide a phonograph pick-up having a noveland distinctive appearance.

Another object is to provide a phonograph I pick-up of the above typewhich may be easily manufactured, assembled, and adjusted, and in whichelements whichbecome worn or defective may be readily replaced at smallcost.

Another object of the invention is to provide an improvedelectro-optical pick-up device comprising a tone arm with a pick-up headat one end thereof, and a translating system completely carried by thesaid head.

A further object of the invention is to provide an improved pick-updevice having novel structural features by which certain desirableresonance characteristics are imparted to the device.

Still another object of the invention is toprovide a pick-up deviceembodying various novel structural features which mutually cooperate toimprove the structure as a whole and which impart desirablecharacteristics thereto.

Other specific objects of the invention will be made apparenthereinafter.

The invention may be clearly understood by reference to the accompanyingdrawings, in which:

Fig. 1 is a plan view of the device disposed adjacent the outer edge ofa record;

Fig. 2 is a plan view of the device with the cover removed from thepick-up head;

Fig. 3 is an elevational view of the device showing the mountingthereof;

the pick-up head;

Fig. 4 is a detail sectional view ofthe cover for Fig. 4a is a viewshowing the rear of the cover for the pick-up head;

Fig. 5 is a perspective view of a novel part employed on the said cover:

Fig. 6 is a perspective view .of certain mounting elements employed;

Fig. 7 is a detail sectionalview taken along line '|--'I of Fig. 3;

Fig. 8 is a perspective view of the slldable carriage for thecounterbalancing weight;

Fig. 9 is a sectional view taken along line 9-9 of Fig. 2;

Fig. 10 is a transverse sectional view of the mounting structure for thepick-up element;

Fig. 11 is a face view of the said structure;

Fig. 12 is a plan or top view of the said structure;

Fig. 13 is an elevational view of the same taken from the right-handside of Fig. 11;

Fig. 14 is a sectional view taken through the center of the saidmounting structure;

Fig. 15 is an exploded view showing the parts of the said structure;

Figs. 16 and 17 are elevational and plan views, respectively, of thestylus and its supporting e view of a certain part Fig. 23 is asectional viewtaken through the central part of the light cell assembly;

Fig. 24 is an exploded view illustrating certain parts of the saidassembly;

Fig. 25 is an electrical diagram illustrating certain features of theinvention by .way of electrical analogs; and

Figs. 26' to 29 are explanatory frequency response curves.

Referring first to Figs. 1 to 3, the phonograph pick-up device providedby this invention comprisesgenerally a tone arm I which is adapted forpivotal and swivel mounting on a suitable support 2 and which is formedatits free end to provide a pick-up head, designated generally byreference character 3. An electro-optical translating system, thedetails of which will be described later, is completely carried by thehead 3 and serves to translate the vibrations picked up from a recordinto electrical currents which are preferably supplied to an amplifyingstage or stages prior to the translation of said currents into sound bya sound reproducer or loudspeaker.

Fig. 18 is a detail sectional view of the stylus support for thecounterbalancing weight.

bracket I3 is attached to plate l2 and pivotally The pick-up head 3includes a generally triangular plate 4 which is formed integrally withthe tone arm. The various components of the translating system aremounted on the supporting plate 4, as illustrated in Fig, 2,

The pick-up device as a whole is preferably shaped generally asillustrated most clearly in Fig. 1, the mounting point of the tone armbeing disposed at 5. The device is shown adjacent the outer edge of arecord 6, and it is to be understood that in operation the free end ofthe tone arm moves inwardly with respect to the record. The particularshape of the device, and especially the shape and arrangements of thetone arm and head, enables the attainment of certain desirable featuresto be mentioned hereinafter.

As shown in Figs. 1 and 4, the pick-up head is provided with a removablecover 1 which is preferably formed of a molded light translucentmaterial. In operation, the entire head is illuminated by light emittedfrom the light source constituting a part of the translating system andmentioned hereinafter. The body of the cover 1 has an opening 8 thereinto accommodate a resiliently mounted button 9. This button is alsoformed of translucent material, but it has a distinctively differentlight-transmitting characteristic than has the body of the cover, sothat the button stands out by contrast. The contrast is preferablyobtained by the use of differently colored materials, for example, thebody of the cover may be white, while the button may be red. The buttonis carried by a resilient spring metal piece II) which is pivotallysecured to the cover at II. By this arrangement, a distinctive andattractive appearance is imparted to the illuminated head duringoperation and, as will be noted hereinafter, such an arrangement permitsadjustment of the pick-up under operating conditions.

Referring now to the tone arm mounting as best illustrated in Figs. 3,6, and '7, a mounting plate I2 is secured to the tone arm, and serves asa part of the tone arm mounting and also as a A 'said transverse openingaccommodates a collar is and a similarly formed nut member H! which aresecured within the said opening by means of a screw 20. As shown in Fig.'7, these members are cut away to conform to the shaft I6, and they gripthe shaft so as to mount the tone arm firmly on the upper end of theshaft. The tone arm is thus supported on collar 15 and shaft l6 which inturn, are mounted on the support platform 2 by means of the bearing 2|and the support structure 22. Bearing 21 should preferably be of theball bearing type so that the tone arm may freely move over the record.

The counterbalancing weight 23 (see Fig. 3) is adjustably mounted on thesupporting plate I2 by means of a suspending carriage element 24 (seeFig. 2). The plate I2 is slotted as shown at 25 in dotted outline inFig. 2. and the extending ears 26 on the element 24 are disposed withinthe slotted portion ofthe plate and thus serve to slidably mount thecarriage element. The counterbalancing weight 23 is resiliently securedto the carriage element 24 by means of a resilient grommet and a screw21. By means of this adjustable mounting of the counterbalancing weight,the pressure on the stylus may be varied at will. To minimize the weightrequired in the counterbalance, most elements in the pick-up arepreferably made of a light material such as aluminum. This will beapparent from Fig. 3, wherein the record is again shown at 6 mounted onthe usual tum-table 28.

Referring now to the translating system mounted on the pickup head, (seeFig. 2) this comprises a lamp and lens assembly 29, a light-sensitivecell assembly 30, and a vibratory armature structure 3| which serves tovary the light impinging on the light cell, as will be more clearlyunderstood later. Referring first to the armature structure, this isillustrated in detail in Figs. 9 to 18. At the apex portion of thetriangular supporting plate 4, there are two upturned supporting lugs 32upon which the armature structure is mounted. This structure comprises apair of frame members 33 and 34 which are rigidly secured to the lugs 32by means of fastening screws 35. (See Fig. 10.) The upper and lowertransverse portions of both of the frame members 33 and 34 are formed toprovide yokes 36 and 31 which serve to support the vibratory armature38. The armature carries a light-reflecting mirror 39 disposed centrallywithin the frame members, and the end or bearing portions of thearmature are supported by bearings 46 and 4|. (See Figs. 14 and 15.)

The bearings 46 and 4| serve to support the armature assembly forvibratory movement, and to this end the bearing elements are formed ofresilient material held in position in the yokes 36 and 31. The upperbearing member 46 is preferably circular in shape, while the lowerbearing member is of square shape. Correspondingly the upper yokes 36 ofthe supporting frames are provided with a circular recess 42, while thelower yokes 31 are provided with rectangular recesses 43. The upper endof the armature is of cylindrical shape, as shown at 44, while the lowerend of the armature'assembly is of square formation, as shown at 45. Thesquare end 45 serves, of course, to normally maintain the mirror andcrank arm in proper relation to the tone arm. (See Fig. 15.)

At the lower end of the armature assembly there is mounted asemi-resilient arm 46 which extends laterally from the axis of thearmature. Further, the arm 46 is bent, as shown clearly in Figs. 14 and16, so that the free end portion of the arm is disposed below the lowerend of the armature. At its free end the arm 46 carries the pick-upstylus or needle 41. The stylus is preferably a sapphire element carriedby a metallic mounting rivet 48 which in turn is mounted on the arm 46.

This assembly (see Fig. 18) is obtained by first placing the styluswithin a soft metal rivet, for example, an aluminum rivet, which has acentral hole of slightly larger diameter than the diameter of thestylus. The crank arm may then be placed loosely on the rivet. Theseelements may now be placed in a mandrel and the rivet may be formed tothe shape indicated in Fig. 18. This operation tightly clamps the stylusinto the rivet without exerting too great a pressure on any portion ofthe stylus, which might break the stylus, and it also clamps the rivetinto the arm, as illustrated.

The resilient arm 46 acts in the manner of a crank arm and serves totranslate the lateral displacement of the stylus by the record intorotary motion of the armature. In operation, the arm 46 is also subjectto a torsional strain and the arm serves as a part of a mechanicalresonance system, the other elements of which are constituted by'thearmature and its bearings. This mechanical resonance feature is animportant part of the inventionland will be described in detail later.At the upper end of the armature there is preferably employed anauxiliary damping member 49 (see Fig. 14) in the form of a small vaneformed of a suitable material, such as viscaloid. This elementconstitutes an additional component in the mechanical resonance system,as will be described later. I

As stated, the arm 46 is semi-resilient. Nor.. mally when the tone armis on the record, the arm and stylus will be in a. position generally asshown in Fig. 14. However, should excess weight be placed on the tonearm head, or should the tone arm be accidentally dropped onto a hardsurface, the arm 46 will flex.

In order to protect the pick-up stylus, there is provided a guard member50, which is secured to the lower part of the armature supporting frameon the outer side thereof. This guard member has an outwardly extendingportion which surrounds the stylus and serves to protect the same bypermitting the stylus to be retracted within the guard when the arm 46is flexed as above described. For example, in case the tone arm wereaccidentally dropped, the stylus would recede into the guard and thelatter would absorb all shock. Details of the operation of the abovedescribed armature will be discussed hereinafter.

Referring now to the lamp and lens assemblythis entire assembly ismounted within a casing or housing 52 (see Fig. 19), which is adjustablysupported by a bracket 53, as shown in Fig. 2. At its forward end, thebracket 53 has a slotted extension which is movably secured to thesupporting plate 4 by means of rivets 54 and 55 which extend through theslots in the extension. At

its other end, the bracket 53 has a slotted extension 53, which ismovably secured to the supporting plate 4, by means of the rivet 51. Therivets 54, 55 and 51 are provided with friction washers to aid inholding bracket 53. Intermediate its ends, the bracket 53 has anintegral turned-up lug 58 with a threaded aperture thereon toaccommodate the end of an adjusting screw 59. The forward end of thescrew is loosely supported by a slotted flange 50 at the outer edge ofthe supporting plate 4. A coiled spring 6| surrounds the shank of thescrew between the lug 58 and the flange 60, and serves to maintain thebracket 53 in any adjusted position thereof. By rotating the screw 59,the bracket 53 may be caused to swing about its pivot points, thereby toadjust the position of the lamp and lens ascent the normal position ofthe lamp. These openings are indicated by the dotted circle 64, in Fig.2. A light-diffusing member 65 of translucent material is carried by thebracket 53 and extends above the upper opening in the lamp casing so asto diffuse the light transmitted through the opening 64 so as to moreevenly illuminate the entire translucent cover plate.

The supporting plate 4 has an elongated opening shown in dotted outlineat 66 in Fig. 2. This opening is adjacent the lower opening in the lampcasing and serves to emit light downward on to the record. Thus theportionof the record adjacent the pick-up head is illuminated, therebyfacilitating the manual positioning of the pickup element on the record.The openings in the casing 52 and plate 4 also serve in cooperation withsuitable openings in the rear wall of the cover 'I to provide for theventilation and cooling of the lamp (see Fig. 4a)

As shown clearly in Figs. 19 and 20, the forward end of the lamp casing52 is formed so as to retain the foremost lens 61. A second lens 68 isdisposed within the casing in spaced relation to the lens 61, by meansof a spacing and retaining collar 69. A second collar 10 frictionallyengages the wall of the casing, and serves to maintain the lens assemblyin place therein.

The lamp II is carried by a conventional socket 12 which is supported bya resilient sleeve 13. The sleeve may be formed by any resilientmaterial, such as soft rubber. It is movably disposed within the openend of the casing and is adapted To maintain its position by virtue ofits frictional engagement with the casing wall. Thus, by means of thismounting, the position of the lamp relative to the lens assembly may beadjusted simply by moving the resilient mounting sleeve 13. Theelectrical connections to the lamp, by means of which it is energized,are of simple conventional form, as shown in Fig. 19, and require nodetailed description.

It will be noted that the lamp filament I4 is preferably substantiallystraight, and by rotating the, lamp mounting, this filament may bealigned vertically with the mirror 39. together with the filament,provides a light beam of generally rectangular shape. In Fig. 20 theopening in the end of the lamp casing 52 is shown generally rectangularso as to serve as a partial mask so that stray light rays reflected bythe base of the lamp and the interior of the casing 52 will beintercepted. This is an important feature since these reflected rays arenot properly focused by the lens system and hence would deleteriou-slyaffect the operation of the device. Further, for increased life andefliciency, the lamp H is preferably of the gas-filled type. In orderthat the lamp will have no objectionable flicker it is preferably heatedby a high frequency power oscillator which may be a part of theaccompanying amplifier.

Referring now tothe cell assembly, there is rigidly mounted on thesupporting plate 4, a bracket 15, which serves to support the entirelight-sensitive cell structure. As shown in Fig. 21, this bracket hasside portions 16 between which the cell support block 11 is carried. Theblock TI is formed of suitable insulating material, and it is recessedto receive the light-sensitive element or cell 18. The cell 18 ispreferably a barrier photocell and may be the well known selenium cell,but, of course, any suitable type of cell may be used. A metallic mask19 is disposed at the front of the cell support, and in addition toserving as a light mask, this member serves also as a retaining meansand as a front contact for the light cell. To this end the member 19 hasextending resilient hook-like arms 80, which are interloekable withcomplementary portions 8| of the supporting member 11, as shown in Fig.23. The mask member 13 also has inturned ribs' 82, whichafford goodelectrical contact with the front surface of cell mem.

The lens system,

her I8. Member I9 also has a laterally extending terminal lug .83 forelectrical connection thereto. In order that the arm 89 of member I9will not engage the end surfaces of the cell I8, insulating members 86,as shownin Fig. 22, are preferably positioned beneath the arms 89.

At the rear of the cell member 18, there is provided a resilientretaining member 84 which serves to hold the cell member I8 in snugengagement with the ribs 82. A terminal lug 85 is secured to theretaining member 84 and constitutes the rear contact for the cellmember. Thus, the cell-member I8 is firmly mounted by means of themembers I9 and .84 and electrical connection is made to the cell memberby means of the extending terminal lugs 83 and 95.

In the intended operation of the device, it is desired that the lamp IIand the bracket 53 be so adjusted that the beam of light reflected bythe'mirror 39 will fall on the cell assembly in such a manner that apart of the beam falls on one of the side members of the mask I9.Further, the light beam should be so focused as to form a clearlydefined spot on the cell assembly. To the end of obtaining theseadjustments, the above-described construction has been found mostuseful. First, the light beam' may be focused to give the desiredsharply defined and properly aligned spot on the cell assembly byadjusting the lamp relative to the lens assembly by means of theresilient sleeve I3. Then, to properly laterally position the focusedspot relative to the mask I9 so that about one half of the spot willfall on the cell proper. the adjusting screw 59 'may be utilized. Inthis connection, the slotted ends 54 and 56 of member 53 cooperate withthe rivets 54, 55, and 51, so that, on adjustment of the screw 59, themember 53 will move as if pivoted about the axis of the armature 38 andthe mirror 39. With this method of adjustment the sharpness of the lightspot on the cell will not be affected by a lateral adjustment of themember 59. I

In making the adjustment of the light source and lens assembly by meansof the screw 59 it is desirable that all extraneous light, such asdaylight, be excluded. The arrangement best shown in Figs. 1, 4 and 5has been found satisfactory. The button 9 is resiliently and pivotallymounted upon the cover I. so that it may be readily displaced to theposition shown by dotted lines in Fig". 1. With the button in thisposition a clear view of the light sensitive cell may be had while theadjustment is being made as herein described. 1

As previously mentioned, the pick-up of this device embodies a novelmechanical resonance system. Mechanical resonance is desirable inpick-up devices of this type because it provides for mechanicalamplification of the higher audio frequencies to compensate for thefalling off of the response of certain components of the pickup.Furthermore, the provision of mechanical resonance is a desirable methodof attaining a sharp cut-off in the response of the pick-up for thepurpose of eliminating noise and needle scratch.

The general functioning of a pick-up of the type above described isrelatively simple. As above described, a light beam is focused on thephotocell. Then the pick-up is placed on a recording. Since the completetone arm of thepick-up has considerable mass as compared .to thevibratory armature the undulations of the record groove will" laterallydisplace the stylus and rotate the mirror relative to the tone arm. Thisof course, will vary the area of the photocell which is illuminated bythe light beam.

In a light-reflecting device of the type here involved, the change inthe illumination on the light-sensitive cell is proportional to themirror displacement, and with the mirror oscillating at any onefrequency the current output of the barrier cell employed will begenerally proportional to the change in the illumination. However, for aconstant amplitude of mirror oscillation the output of a barrier cellwill decrease with increasing frequencies of mirror oscillation, andthus for mirror oscillations having a constant amplitude and variablefrequency, the output of the device will decrease seriously at higheraudio frequencies. in the pick-up, the motion of the mirror is caused toincreasingly exceed that corresponding to the lateral displacement ofthe stylus as the frequency increases up to the resonant frequency,above which the motion of the mirror decreases sharply. This resonancecharacteristic may, therefore, be used to compensate at least partiallyfor deficiencies in the natural response of the pick-up resulting fromthe use of elements having a non-uniform frequency characteristic overthe desired frequency range.

Referring to the physical makeup of the meof special synthetic rubbersuch as neoprene.

The mass of the armature is preferably made as small as is practical.may be made of aluminum while the crank arm 46 may be phosphor bronzespring material. The operation of this mechanical system and the resultsobtained thereby may be seen clearly by considering an electricalanalogy as depicted in Fig. 25.

Fig. 25 shows an electrical circuit diagram comprising elementsgenerally analogous to the components of the pick-up. In this circuit,current represents velocity and charge represents displacement. Mm is aninductance representing the mass of the vibrating mirror and armature.Cc and Cb are capacitance representing, respectively, the compliance ofthe crank arm 46 and the complianceof the resilient bearings 40 and M.Rb is a resistance representing the internal friction of the armaturebearings. Similarly, Mv, C'v, Rv represent, respectively, the mass,compliance, and resistance of the viscaloid damping vane 49. It shouldbe noted that all of these last three elements are indicated grouped andvarithe velocity thereof. Hence, the displacement of the mirror in aresonant system may exceed By providing mechanical resonance To thisend, the armature.

the displacement'in a non-resonant system; thatis when the compliance Cois not present.

The response characteristic, over the audio frequency range, of thephonograph pick-up device is illustrated in Figs. 26 to 28.

Fig. 26 shows the cell output which would be obtained if the stylus wereoscillated at constant amplitude over the audio frequency range in apick-up having a non-resonant mechanical system.

The curve in Fig. 27 shows the output of the cell which is obtainedunder the same'cDnditiDns employing a suitably resonant mechanicalsystem, such as that of the present device.

Fig. 28 is a curve showing the ratio of the angular displacement of thmirror with respect to the angular displacement of the crank arm 48. Thecurve of Fig. 28 is derived by subtracting the curve of Fig. 26 fromthat of Fig. 27. This shows how the high frequency response ismaintained by the use of mechanical resonance. The importance of thisfeature will be understood if it is realized that, to obtain a uniformand pleasing response in a pick-up without mechanical resonance, itwould be necessary to decrease the low frequency response of either thepick-up or the accompanying amplifier. To do this would, of course,undesirably decrease the output of the system throughout the entireaudio frequency range. Thus, the use of mechanical resonance makespossible increased output over the entire audio frequency range of thepick-up with any given amplifier.

In addition, the use of resonance provides for a sharp cut-oil of theresponse characteristic. This cut-off substantially eliminates needlescratch and other undesired high audio frequency noises which mightcause cross modulation in the attendant amplifying system to which thepick-up is connected.

However, it will be understood that the above described response curvesmust be modified when a recording other than a constant amplituderecording is used. For example, most records now in common use are ofthe constant velocity type. That is, the lateral movement of the needletakes place at a constant velocity independent of fre-' quency. As aresult, with these recordings the amplitude of the displacement of theneedle decreases with increasing frequencies.

As a result, if the pick-up were used with these recordings thedisplacement of the needle would not be constant and independent offrequency and the response would not be as shown in Figs. 26 and 27.Instead, the output would decrease with frequency, as shown by Fig. 29.This falling response makes necessary the use of a compensatingelectrical amplifier connected between the pick-up and thesoundreproducing device to restore the overall response of the pick-upand amplifier to that shown by Fig. 27. Nevertheless, the increasedoutput of the pick-up by reason of the employment of the resonantmechanical unit greatly simplifies the problems of amplifier designsince any output gained in the pick-up itself need not be compensatedfor in the amplifier.

Returning again to a consideration of Figs. 1, 2, 11, and 12 it will beseen that the tone arm and head are arranged so that one side of thetone arm conforms generally to the shape of the record edge. Further,the head. of the pick-up is offset with respect to the tone arm so thatthe armature and stylus are brought close to the record edge. This is adesirable and important feature, particularly when the pick-up is usedin "conjunction with an automatic record changer,

for this arrangement materially decreases the rotation of the pick-upabout the pivot 5' which.

is required to position the tone arm clear of the record after theplaying thereof. In addition, the arrangement decreases the spacerequired for operation of a record changer using the pick-up.

However the above described arrangement makes necessary the angularrelation between the mirror 39 and the crank arm 46 shown in Figs. 11and 12. That is, the crank arm 46 must be arranged with such a relationto the armature and tone arm that the longitudinal axis of the crank armwill normally pass through the axis of the tone arm pivot 5. When thestylus v is on a recording, the friction and drag will cause the crankarm to tend to move so that its longitudinal axis is coincident with thedirection of the forces due to friction, and because of the resilienceof thearmature bearings, the motion of the armature may be sumcient todisplace the light beam so as to render the pick-up inoperative. If theaxis of'the crank arm passes through the tone arm pivot, however, nosuch trouble will be encountered. Primarily for this reason thearrangement of crank arm and armature shown in Figs. 11 and 12 is to bepreferred.

The pick-up as above described greatly reduces record wear as comparedwith conventional devices for the' principal reason that the energyrequired to vibrate the armature is very small even at the higher audiofrequencies. As a result the grooves of a recording are required toprovide only a very small driving force. Further, it is possible withthis type of pick-up to balance the tone arm so that only avely smallpressure need be exerted on the needle. For example, a needle pressureof one ounce or even less has been found satisfactory. With such a lowneedle pressure, the Wear on the stylus is also materially reduced andthe normal life thereof is increased about four times.

From the foregoing description, it will be seen that the pick-up deviceprovided by this invention embodies various novel features whichmutually contribute to improve the device as a whole. While a singleform of the device has been illustrated and described for the purpose ofdisclosure, it will be understood that various modifications,particularly in the matter of details, may be resorted to withoutdeparting from and means for diffusing the light from said source,

whereby said light source serves additionally to substantially uniformlyilluminate said cover.

2. In a pick-up device for phonographs, comprising a tone arm, a head atone end of said tone arm, an electro-optical translating systemincluding a light source and a light-sensitive means responsive to thelight from said source all carried by said head, a translucent covermember enclosing the elements of the translating system, and means fordiffusing the light from said source, whereby said light source servesadditionally to substantially uniformly illuminate said cover, said headhaving an opening therein below said light source and positioned toilluminate a recording, said cover member having at least one openingtherein, said openings serving cooperatively to provide for theventilation and cooling of said head.

3. In a phonograph pick-up device comprising a tone arm, a head at oneend of said tone arm, an electro-optical translating system including alight source and lens assembly, a light sensitive means, and a vibratoryarmature arranged to reflect light from said source onto said lightsensitive means and to modulatethe light supplied to said lightsensitive means, the longitudinal axis of said assembly passing throughthe axis of said armature, and means for adjusting the relativepositions of said assembly and said light sensitive means whereby tolaterally adjust the reflected light on said light sensitive means, saidadjusting means constructed and arranged to rotate said assembly in suchmanner that the longitudinal axis thereof will continuously pass throughthe axis' of said armature throughout the range of adjustment.

4. In a phonograph pick-up device comprising a tone arm, a head at oneend of said tone arm, an electro-optical translating system including alight source and lens asembly, a light sensitive cell assembly and avibratory armature arranged to reflect light from said source onto saidcell and to modulate the light supplied to said cell, and means foradjusting the relative posiitons of said assemblies whereby to laterallyadjust the reflected light on said cell, said adjusting means includingmounting means for said light source and lens assembly, arranged torotate in such manner that the longitudinal axis of said assembly willcontinuously intersect the axis of said armature throughout the range ofadjustment.

5. In a sound pick-up device for phonographs, a tone arm having apick-up head, a cylindrical lamp casing mounted on said head, a lampwithin said casing, a plurality of spaced lenses within said casing,lens spacing and retaining collars arranged in operative associationwith said lenses within said casing, said casing being formed tolight-responsive device, said means comprising a' support, a vibratoryarmature carried by said support, an arm extending laterally from thelower end of said armature, a stylus mounted at the free end of saidarm, saidfree end of said arm being defiectible upwardly, andlightrefiecting means carried by said armature.

8. In a sound pick-up device for phonographs, a tone arm having apick-up head, a lamp, and a light-responsive device mounted on saidhead, and pick-up means carried by said head in cooperative relationwith said lamp and said lightresponsive device, said pick-up meanscomprising a support, a vibratory armature carried by said support,resilient bearing means for said armature, a compliant arm extendinglaterally from the lower end of said armature, a stylus mounted at thefree end of said arm to vibrate said armature through said arm, andlight-reflecting means carried by said armature, the compliance of saidbearing means and said arm and the mass of said armature being socorrelated as to effect mechanical resonance over the upper portion ofthe frequency range of the device.

9. In a sound pick-up device for phonographs, a tone arm having apick-up head, a lamp, and a light-responsive device mounted on saidhead,

and light-controlling means carried by said head provide a mask at itslight-emitting end, a light-] responsive device on said head adapted toreceive light from said lamp, a vibratory armature element on said headadapted to modulate the light supplied to said lighteresponsive device,and means for adjusting said lamp casing to control, the amount of lightimpinging on said lightresponsive device without changing the focus ofthe light beam.

6. In a phonograph pick-up device of the electro-optical type, a lightsource and lens assembly comprising a tubular member having itslightemitting end formed'to provide a mask, a lens disposed within said'end, a retaining collar arranged to frictionally engage said tubularmember to retain said lens in said member, a light source within saidmember, mounting means for said light source comprising a resilientbushing adapted to engage said member, whereby said light source may bereadily adjusted relative to said lens and whereby said lens and saidlight source may be readily removed from said member for inspection orreplacement, and means for adjusting said member to vary the position ofthe light beam without changing its focus.

7. In a sound pick-up device for phonographs, a tone arm having apick-up head, a lamp, and a light-responsive device mounted on saidhead,

and light-controlling means carried by said head in cooperative relationwith said lamp and Sai in cooperative relation with said lamp and saidlight-responsive'device, said means comprising a support, a vibratoryarmature carried by said support, resilient bearing means for saidarmature, a damping element mounted at the upper end of said armature, acompliant arm extending laterally from the lower end of said armature,

and a stylus-mounted at the free end of said arm to vibrate saidarmature through said arm, the compliance of said bearing means and saidarm, the mass of said armature, and the compliance and mass of saiddamping element all being so correlated as to effect mechanicalresonance over the upper portion of the frequency range oi the device.

10. A self-contained armature unit for a phonograph pick-up device,comprising a pair of juxtaposed open frame members having complementalrecesses forming aligned bearing retainers on opposite portions of saidmembers, resilient bearing elements seated in said retainers, anarmature supported by said bearing elements, a mirror mounted on saidarmature within the open frame members, a deflectible crank armextending from one end of said armature, a stylus carried by saidcrankarm, a guard for said stylus integral with one of said framemembers, and means for removably securing said frame members togetherand for securing all of the aforesaid elements together as anindependent unit.

11. A phonograph pick-up device, comprising a hollow tone arm, a rigidplatform at the free end portion of said arm, said platform being ofplan form diminishing in width and reaching an apex toward the free endof the tone arm, an oscillatory reflecting armature mounted on saidplatform at the said apex, a light beam-producing means and alight-responsive means on a wider part of said platform in cooperativerelation with said reflecting armature, and a stylus at said apex foractuating said armature to thereby vary the light impinging on saidlightresponsive means according to undulations of a record groove.

12. A phonograph pick-up device, comprising a horizontally-extendinghollow tone arm having a relatively small vertical dimension, a rigidplatform carried by the free end of said tone arm and extending from thelower edge portion thereof, a photoelectric translating system carriedby said platform, the component parts of which have a vertical dimensionsubstantially coextensive with the vertical dimension of said tone arm,and a cover enclosing the component parts of said translating system,whereby there 10.

is provided a compact and shallow translatin unit at the end of the tonearm having a vertical dimension comparable to that of the tone arm.

13. A phonograph pick-up device, comprising a light-weight tone arm, apivotal mounting for 15 said tone arm which permits movement of a freeend portion of the arm relative to a record in playing position, saidarm being subject to vibrations which may be transmitted thereto throughsaid mounting, a rigid plate at the free 2 end portion of said arm, avibratile stylus carried by said plate so as to engage said record, andan electro-optical translating system operable by said stylus and havingall of the com- 14. A phonograph pick-up device, comprising alight-weight ton'e arm, a pivotal mounting for said tone arm whichpermits movement of a free end portion of the arm relative to arecord inplaying position, said arm being subject to vibrations which may betransmitted thereto through said mounting, a rigid plate at the free endportion of said arm, said plate being of plan form diminishing in widthand reaching an apex toward the free end of the tone arm, a vibratilestylus at said apex, an oscillatory reflecting armature operable by saidstylus, a light beamproducing means and alight-responsive means on awider part of said plate and relatively adjustable crosswise of theplate, said plate by reason of its rigidity effectively preventing anyvibrations in the tone arm from adversely afiecting the operation of thetranslating system.

15. In a sound pick-up device for phonographs,- a tone arm, a head atthe end of said tone arm, an electro-opticai translating systemincluding a light source carried by said head, and a cover enclosing thtranslating system, said head having an opening therein below said lightsource ponent parts thereof mounted on said plate, said 25 to illuminatea recording.

plate byreason oiI its rigidity efiectively preventing any vibrations inthe tone arm from adversely affecting the operation of said translatingsystem.

ELMER O. THOMPSON.

